The present invention relates to an underwater pump and particularly to a tandem pump which is provided with two symmetrically disposed pump units. To each pump unit can be attached a different or similar water processing accessory; and each pump unit is provided with a volume adjusting device having a plurality of engagement protrusions disposed on the underside periphery thereof and selectively engaged with a plurality of corresponding retaining recesses disposed on the top periphery of a control device so as to produce click sound as the adjusting device is actuated to vary the volume of the flow.
There are a plurality of first communication ports disposed on the control disc and defined in conformance to a plurality of second communication ports disposed on an adjusting board. By turning the control disc against the adjusting board, the first and second communication ports can come into full alignment with or go fully out of alignment with each other or at positions in between, resulting in the variation of volume of the inlet water.
As shown in FIG. 1, the conventional water pump has only one pump unit which is made up of a motor 1A, a propeller 3A having a plurality of blades 31A, a top adjusting means 32A, a control chamber 33A having a control slide door 35A and a bottom adjusting disc 34A , and a filter accessory 36A which is associated with the pump. It can be clearly seen that the prior art pump has only one water inlet 341 and outlet 332 and the volume control means uses merely one port and the water volume can be controlled by turning the bottom disc 34A against the control chamber so as to vary the degree of the alignment of the port 341 and one of the ports 331 of the control chamber 33A.
The prior art pump can be engaged with only one water processing accessory, and it becomes inconvenient as more than one accessory is required in one aspect, and the volume adjusting means is designed in such a manner that it is not effectively operated in another aspect.